This disclosure relates to color printing systems. Specifically, this disclosure relates to methods and systems for mapping in-gamut and out-of-gamut colors.
In the field of printing, printer profiles are used to determine device-dependent colorant values needed to make a specific color. These printer profiles contain multidimensional transforms that map device-independent (or calorimetric) values to device dependent values and vice versa. For example, a three colorant printing device generally includes cyan, magenta and yellow (C, M, Y) colorants in the form or toner, ink or dye. The printer profile would comprise a multidimensional transform in the form of a 3-D lookup table (LUT) that maps a plurality of input 3D calorimetric signals to CMY device values that will produce the requested input calorimetric signals when printed to the given device. Alternatively, the printer profile may be applicable for a four colorant printer that also employs black (K) in addition to C, M, Y. In this case the 3D LUT maps 3D input colorimetric signals to CMYK device values that will produce the requested input colorimetric signals when printed to the given device. A similar reasoning applies for other types of printers, including ones that employ special colorants in addition to the four standard CMYK colorants, such as orange (O), violet (V), and green (G).
One method of building a LUT is to use an iterative controls technique to search for the device dependent colorant values, e.g. CMYK values, for each node in the LUT until the desired color at that node is achieved. The search could take place either by iterating on the real printer or by iterating on a printer model that accurately reflects the color characteristics of the real printer. An important observation is that a substantial fraction, most often the majority, of the nodes in the LUT corresponds to colors the printing device cannot print. These colors are referred to as out-of-gamut colors.
One approach to determining device dependent colorant values for out-of-gamut colors is to simply map the out-of-gamut color to in-gamut colors, and then carry out the iterative search process for the mapped in-gamut colors.
One disadvantage associated with an iterative method of mapping out-of-gamut colors to in-gamut colors is the number of measurements required. In other words, iterative methods typically include multiple measurements to iteratively narrow in on a desired outcome.
This disclosure provides an alternative method and system for determining in-gamut and out-of-gamut values for a LUT that involves substantially fewer iterative search calculations.